Metallic paint

ABSTRACT

AN IMPROVED COATING COMPOSITION ADAPTED TO YIELD A FINISH HAVING AN APPEARANCE AND TEXTURE SIMILAR TO THAT OF A MECHANICALLY FINISHED METAL SURFACE IS PROVIDED WHICH INCLUDES A SUITABLE FILM-FORMING VEHICLE AND AN IMPROVED PIGMENT. THE PIGMENT COMPRISES FINELY DIVIDED NON-LEAVING FLAKE ALUMINUM PARTICLES IN A SIZE DISTRIBUTION RANGING FROM APPROXIMATELY 30 MICRONS TO APPROXIMATELY 200 MICRONS; A NATURAL OR SYNTHETIC PEARL SIMULATING AGENT; AND LARGE, INERT PARTICLES OF SILICA GEL, ALL OF WHICH ARE DISTRIBUTED THROUGH THE COATING. A TRACE AMOUNT OF YELLOW TONING PIGMENT SUCH AS BURNT SIENNA MAY ALSO BE INCLUDED.

United States Patent 3,708,318 METALLIC PAINT Donald R. Reinhart,Cockeysville, and Russell A. Fritts, Phoenix, Md., assignors toConchemco, incorporated, Kansas City, Mo. N0 Drawing. Filed Aug. 18,1970, Ser. No. 643M Int. Cl. C08g 51/04 US. Cl. 106193 M 19 ClaimsABSTRACT OF THE DESCLOSURE This invention relates to improved finishesfor metal castings and is specifically directed to an improved paint andpigment therefor which produces a bright, durable metallic finish.

At the present time, metal castings which are used as the outer housingsfor tools and appliances subjected to heavy duty professional use inindustrial or commercial environments are frequently provided with amechanical finish; that is, one achieved by mechanically abrading theexternal surface of the casting. This finish was developed as a resultof a need for adequate appearance in environments where the tools orother appliances are subjected to long term wear in the presence ofgrease, grit, etc. and, frequently, subjected to abusive use either dueto the nature of the job or due to careless handling by the operator.Given all of these conditions, the need is for a tough, durable finishwhich does not get dirty easily, does not easily show scratches or otherabrasions and which, at least when new, is visually attractive.

The mechanical finish which has heretofore been the best availableanswer to these requirements is considerably more expensive than itsmechanical function would require. Specifically, at least the exteriorsurface of the casting must be of high quality since blemishes or minorsurface imperfections are not easily obscured by the mechanical finish;furthermore, the process of mechanically finishing the casting usuallyrequires hand application of each individual casting to a rotating wirebrush. Especially in this case, but also in other forms of mechanicalfinishing, the process is expensive and time consuming and it frequentlyproduces a relatively non-uniform appearance. For example, it isobviously difficult to maneuver a complex casting so that all of therecesses, sloped and curved surfaces, etc. which may be clearly visibleto an observer are subjected to the same amount of abrading by a wirebrush as are received by the flat, broad area major surface portions ofthe casting.

Previous attempts have been made to produce a chemical coating whichwould adequately approximate the desired characteristics of mechanicalfinishes. However,

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these previous attempts have not been successful, largely because thecoatings which can compete in cost with the mechanical finish have notbeen sufiiciently durable. Another reason for this failure lies in thefact that professional users of devices such as portable power toolshave learned to accept the mechanical finish as a standard and,especially because of the many failures of substitute finishes, arereluctant to accept new substitutes which are too obviously differentfrom the mechanical finish to which they are accustomed. It is widelyfelt among such users that painted finishes will never the adquate tofunction in an industrial or commercial environment because they scratcheasily and wear off and because the gloss of a painted finish quicklyreveals abrasions and accumulated dirt. In fact, it is accepted practicein this industry to use the mechanically finished casting only onprofessional tools and to provide a painted surface only on toolsintended for relatively light duty. This distinction is well known tothe users of professional tools and they, accordingly, avoid paintedtools.

In order to provide a chemical coating which can be used on tools forthe professional market, therefore, it is necessary to accomplish twoobjectives. First, the coating must be at least as good in a functionalsense as the mechanical finish and second, its appearance must besufiiciently close to that of the mechanically finished metal so that itis not rejected without being tried by the professional user. Noprevious chemical coating has met these objectives.

Accordingly, it is an object of this invention to provide a new andimproved chemical coating for metallic castmgs.

It is a further object of this invention to provide a chemical finishwhich approximates the characteristics of a mechanically finished metalcasting and which preserves a substantially new appearance for a longerperiod of time than mechanical finishes.

It is also an object of this invention to provide a chemical finish formetal castings which possesses similar functional characteristics tothose of mechanical finishes but which is less expensive.

Another object of this invention is the provision of an improvedcovering which simulates the brightness, color and texturalcharacteristics of mechanically finished metal.

Another object of this invention is the provision of an improved methodof finishing metallic castings.

It is also an object of this invention to provide an improved pigmentfor use in a clear film-forming vehicle which produces brightness, colorand textural characteristics in the film which are similar to those ofwirebrushed aluminum.

Further objects and advantages of this invention will become apparent asthe description and illustration thereof proceed.

Briefly, in accord with one embodiment of this invention, an improvedcoating composition adapted to yield a finish having an appearance andtexture similar to that of a mechanically finished metal surface isprovided which includes a suitable film-forming vehicle and an improvedpigment. In accord with this invention, the pigment comprises finelydivided non-leaving flake aluminum particles in a size distributionranging from approximately 30 microns to approximately 200 microns; anatural or synthetic pearl simulating agent; and inert particles ofsilica gel, all of which are distributed through the coat- 3 ing. Atrace amount of yellow toning pigment such as burnt sienna may also beincluded.

Previous attempts to produce a finishing composition of the typedescribed above have failed for a number of reasons. One difficulty hasbeen that of producing the reflectivity or brightness under incidentlight from any angle which is characteristic of mechanically finishedmetal such as wire brushed aluminum castings. Large aluminum particlescan provide such reflectivity, but previously, such particles in aone-coat system produced a sandpaper-like texture which is notacceptable, particularly in the instance of castings which must behandled such as those for portable power tools. This texturalcharacteristic has limited the maximum size of aluminum particles whichcould be used to a range which does not provide reflectivity but whichonly produces a gray color. Another difficulty in the provision of asuitable pigment is that of providing a light or whitish cast to thegray tone produced by small aluminum particles. The requirement thatsufiicient small aluminum particles be used to make the coating opaqueand thus cover the underlying casting has also produced a darker tone ofgray than that characteristic 'of wire brushed aluminum or othermechanically finished castings.

In addition to these difficulties in simulating the appearance of thebrushed metal, it has not previously been possible to produce thetextural characteristic of brushed metal.

In accord with the present invention, these difficulties are overcome bya unique combination of ingredients which produces a finish very similarto that of mechanically finished castings, in color, brightness andtexture or feel. In addition to reproducing these characteristics ofmechanical finishes, it has also been discovered that this finishenables a substantial reduction in the cost of the casting since thecomposition which produces these characteristics also serves to obscureor hide surface blemishes or minor imperfections such as grinding wheelmarks, small pock marks, etc. Finally, this coating has been foundunexpectedly to be substantially more durable in appearance thanmechanically finished castings.

In general terms, the composition which accomplishes these objectivesincludes first, a suitable film forming vehicle and second, an improvedpigment combination. Any of the conventional transparent film-formingvehicles may be provided such a a chemically reactive or heat reactivevehicle, a nitrocellulose lacquer, or an acrylic alkyd. Of course,suitable solvents and/or diluents for the respective vehicle selectedwould be used. As a specific example, one vehicle which has been used isa heat reactive vehicle such as 72% soya alkyd and 28% Melamine. Thesolvent for this vehicle may comprise 90% aromatic hydrocarbon such asXylol and Toluol combined with butyl alcohol. In the wet state, thesolvent is about 48% by weight of the enamel, the vehicle is about 40.5%by Weight of the enamel and the pigment combination, described below, isabout 11.5% by weight of the enamel.

The improved pigment in accord with the present invention includes, as abasic coloring and reflectivity agent, finely divided particles ofnon-leafing aluminum. The quantity of aluminum present is preferablyfrom to 30% by weight of the pigment. In accord with a specific novelfeature of this invention, the particles of aluminum feature of thisinvention, the particles of aluminum range in size from approximately 30microns to approximately 200 microns. The size distribution is such thatthe smaller aluminum particles provide an opaque, generally gray colorwhile the larger particles provide reflectivity under both high and lowangle incident light which is similar to that of mechanically finishedmetal. As a specific example, the material sold under the trade nameSilvar 02 Non-leafing Aluminum, manufactured by the SilberlineManufacturing Company is suitable.

The exact size distribution of these aluminum particles is not critical.Generally, sufiicient small particles should be included to produce thedesired metallic gray appearance and to make the film opaque; at thesame time, sufficient larger particles must be provided so as to producethe desired reflectivity. As a specific example, the following ditribution, which is that of the Silvar 02, is suitable (the statedpercentages are by weight of the total weight of aluminum): 6% isbetween 140 mesh and mesh to 149 microns); 30% is between 325 mesh andmesh (44 to 105 microns); and 64% is between 400 mesh and .325 mesh (37to 44 microns). Obviously, other distributions could be used which alsowould provide a quantity of glittering highlights in a gray background.It is preferred that at least 4% of the particles be above the 100micron level to adequately approach the glitter of a mechanicallyfinished metal. Particles above 200 microns produce too rough a surface.

The second ingredient in the novel pigment combination of this inventionis a finely divided amorphous silica gel, preferably present in anamount ranging between 8 and 14% by weight. Among the significantcharacteristics of these particles are that they be inert in the filmforming vehicle and solvents used, that they not significantly affectthe metallic appearance provided by the rest of the pigment, that theyremain substantially uniformly dispersed in the vehicle during and afterapplication and that they be of suitable size to have a smoothing effectand reduce the roughness produced by the large aluminum particles.Specifically they must not dissolve, break up or swell in the enamel asis characteristic of previously used flatting agents. As a specificexample, the silica gel manufactured and sold under the trade nameSyloid 620 by the Davison Chemical Division of W. R. Grace & Company issuitable.

The function of these particles of silica is of particular importance inthis combination. Although siliceous materials have previously been usedas colloidal fiatting agents to reduce gloss, it has not previously beenrealized that substantially larger, inert particles can be used for adifferent function. Specifically, the particles used in the practice ofthis invention should be at least 10 microns in diameter and preferablyabout 20 microns in diameter. The function of these particle is toremain inert and mechanically suspended rather than becoming a colloidalsolution. This produces a smoothly roughened or pebbled texture on thesurface and, more significantly, smooths out the sharpness which wouldotherwise be produced by the large size aluminum flakes describedpreviously. Thus, the presence of the silica particles simultaneouslyprovides the desired texture and permits the use of the large aluminumparticles which are needed for reflectivity.

The pigment combination of this invention also includes approximately 30to 80% by weight of the pigment of a pearl simulating agent which servesto add a milkywhite tone to the gray color of the aluminum and tobrighten its appearance. The agent used may comprise any of the knownpearlescent compositions such as the natural extract from fish scales orthe synthetic substitutes therefor such as crystallized mercuricchloride. As a specific, preferred example, the agent manufactured andsold under the trade name Pearl Afllair NF-104-D by E. I. du Pont deNemours and Company is suitable. This material comprises 30-40 micronplatelets of mica coated with titanium dioxide. It functions to whitenthe gray of the aluminum and may add a very light iridescent tone.

Finally, it is preferable to add a very small quantity of a yellowingtoner such as brunt sienna to provide a slightly warmer tone. In fact,wire brushed aluminum has a very slight yellow tint and this is bestachieved by adding about 0.05% by weight of the total pigment of burntsienna. This quantity could vary between 0.01% and 0.1% depending on theappearance desired. In the examples and claims, this range is referredto as a trace amount. Of course, these paints may also include verysmall percentages of slip agents, anti-settling agents, stabilizers orother conventional additives which contribute to practical storage andapplication of a production coating.

In functional terms, the above described pigment combination in asuitable film has been found to provide all of the desiredcharacteristics previously described. Specifically, a metalliccoloration is provided by the combination of small aluminum particlesand the pearl simulating agent. It is noted that pearl simulating agentshave only a very weak effect on the color and therefore, it is necessaryto use the relatively large percentage previously mentioned. Generally,combinations of these ingredients within the indicated ranges providethe warm whitish gray appearance characteristic of mechanically finishedmetal such as aluminum.

At the same time, the use of the large aluminum particles products thepoints of high reflectivity to light of both high and low angle ofincidence which are characteristic of mechanically finished metal. Thepearl simulating agent also contributes to the brightness of the finish.

The inclusion of an inert material such as the silica gel serves anumber of purposes. First, this material fills the interstitial spacesbetween the large aluminum particles and thus smooths the rough texturewhich would otherwise be characteristic of a coating including theseparticles. Secondly, the combination of particles in the mentionedpercentages and sizes produces a surface having a feel very similar tothe textured feel of a mechanically finished casting. Finally, thiscombination of particles including the silica produces a texturedappearance which is similar to that of the mechanically finishedcasting.

The net effect of the use of this pigment combination in a suitable filmis to produce a finish similar to mechanically finished castings; infact, the appearance is so similar that many users cannot recognize itas a painted or chemical finish. In a comparison performed by a Neoteccolorimeter, Colormate 2000 series, model 602D, a sample of a paintedfinish in accord with this invention was found to be within a class 1color tolerance match in side-by-side comparison with a wire-brushedaluminum casting. In another comparison, 50X photomicrographs of suchsamples were visually indistinguishable.

Furthermore, the finish has been found to be substantially improved overa mechanical finish in several functional respects. It has been foundthat this finish is more durable in appearance than mechanical finishessince it is more resistant to light mechanical abrasion and scufling.While the reason for this is not completely understood, it may be due toa cushioning effect provided by the use of the large silica gelparticles and the mica flakes; in any event, tools with this finishmaintain a substantially improved appearance as compared to mechanicallyfinished tools in similar uses. Also of added importance is the factthat the chemical finish is not subject to oxidation as is amechanically finished casting and thus it preserves a uniform appearanceand does not become mottled or discolored due to aging or handling,Finally, the textured feel provides a non-slip surface which is ofsubstantial benefit to the user.

It is noted that the coating of this invention provides a single coatfinish over bare metal which can be applied by any of the severalconventional application methods and either air dried or ba ked,depending on the film-forming vehicle selected. A particular feature ofthis composition is that the various ingredients of the pigment remainsubstantially uniformly dispersed throughout the vehicle during sprayingand drying, thus producing uniform properties in the final finish. Itwill be recognized by those skilled in the art that modifications of thetype and relative quantity of the vehicle and solvents may be made asrequired to accommodate the liquid paint to a particular form ofapplication. The novelty of this invention lies primarily in the uniquepigment combination and secondarily in the provision of a sprayable, onecoat finish.

The specific examples set forth below illustrate the practice of thisinvention in a number of applications; however, it is not meant to limitthe scope of this invention to the specific compositions set forththerein.

EXAMPLE 1 A baking enamel is prepared by mixing the followingcomponents:

Percent by wt. of total Vehicle Soya alkytL- Melamine.

Solvent Non-leafing aluminum flakes, random size, 30-

200 microns Mica platelets coated with titanium dioxide-.. Silica gelparticles, approximately 20 microns. Burnt sienna This paint is appliedby spraying in a ransburgh electrostatic unit and is cured by baking forfifteen minutes at 275 F. This paint has an appearance and texturesimilar to that of a mechanically finished aluminum casting andmaintains its appearance characteristic for a longer time than themechanically finished casting.

EXAMPLE 2 A paint having the following composition is prepared:

200 microns Mica platelets coated with titanium dioxide. Silica gelparticles, approximately 20 microns. Burnt sienna This paint is appliedand dried in a manner similar to that indicated in Example 1. Theappearance of the finished article is similar to that stated in Example1 except that the overall appearance is not as bright as the normalappearance of a mechanically finished casting due to the slight excessof silica particles.

EXAMPLE 3 An air drying paint is prepared by mixing the followingingredients:

Percent by Weight of total Vehicle Styrenated alkyd..... SolventConventional aromatic solvents.- Pigment Non-leafing aluminum flakes,random size, 30-

200 microns 23. 8 Mica platelets coated with titanium dioxide- 64. 8Silica gel particles, approximately 20 microns. 11. 4 Burnt sienna TraceThis paint is applied by spraying to a metallic casting and exposed toair at room temperature until dried. The resultant article has anappearance similar to that described in the case of Example 1 and asimilar texture. The durability of the appearance of this article issomewhat less than that of the paint stated in Example 1 but is stillimproved over that of conventional mechanical finishes.

Percent by weight of total Vehicle 40. 4

Soya alkyd. Melamine Pigment Non-leafing aluminum flakes, random size,30-

200 microns Mica platelets coated with titanium dioxide. Silica gelparticles, approximately 20 microns Burnt sienna This paint, whenapplied by spraying to a metallic casting and dried by baking forfifteen minutes at 275 F., has a similar appearance and texture to thatstated in Example 1 except that the tone of the color is slightlylighter and the number of points of higher reflectivity is somewhatreduced.

As previously noted, these examples are not intended to limit the scopeof this invention to the specific details set forth. For example, it hasbeen determined that the amount of random sized non-leafing aluminumflake can vary between and 30% by weight of the pigment combination; thepearl simulating agent can vary between 30% and 80%; and the inertparticles can vary between 8% and 14%. The relative quantites of theseelements selected in any given combination will depend on the preciseappearance and texture desired. However, it will be found that, as thequantites used go beyond the noted limiting percentages, that thedifference in texture or appearance between the painted article and amechanically finish casting become excessive.

It will be apparent to those skilled in the art that many variations ofthe stated compositions can be made within the ranges set forth withoutdeparting from the objective of providing the above described finish.Accordingly, it is intended that the appended claims cover all suchvariations as come within the true spirit and scope of the invention.

We claim:

1. A coating composition adapted to yield a finish of high durabilityand having an appearance and texture similar to that of a mechanicallyfinished metal surface comprising a polymeric film-forming vehicle and apigment, said pigment consisting essentially of:

(a) from 15% to 30% by weight finely divided nonleafing aluminumparticles, said particles being present in sizes ranging fromapproximately 30 microns to approximately 200 microns;

(b) from 30% to 80% by weight particles of a pearlsimulating agent forwhitening the finish; and

(c) from 8% to 15 by weight particles of silica gel, said particleshaving an average diameter of at least 10 microns wherein said pigmentis present in an amount sufficient to simulate the appearance ofmechanically finished metal.

2. The coating composition claimed in claim 1 wherein said pigment alsoincludes a trace amount of yellow toner.

3. The coating composition claimed in claim 2 wherein said tonercomprises burnt sienna.

4. The coating composition claimed in claim 1 wherein said silica gelparticles are sufficient in size and number to reduce the surfacesharpness produced by said large particles of aluminum.

5. The coating composition claimed in claim 1 wherein said particles ofsilica gel are not less than 10 microns in average diameter.

6. The coating composition claimed in claim 1 wherein said silica gelparticles are present in an amount between 8% and 14% of said pigmentand wherein the size of said silica gel particles is on the order of 20microns.

7. The composition claimed in claim 1 wherein at least 4% of saidaluminum particles are greater than 100 microns in size.

8. The coating composition claimed in claim 7 wherein the sizedistribution of said aluminum particles on a percent by weight basis isin accord with the following schedule: at least 4% is greater than 105microns; at least 25% is between 44 microns and 105 microns; and atleast 50% is less than 44 microns.

9. The composition claimed in claim 1 wherein said pearl simulatingagent comprises platelets of mica coated with titanium dioxide.

10. The coating composition claimed in claim 9 wherein the majordimension of said mica platelets is on the order of 30 to 40 microns.

11. The coating composition claimed in claim 1 wherein suflicient pearlsimulating agent is included in said pigment so as to produce anoticeably white tone in the resultant coating.

12. The coating composition claimed in claim 1 Wherein the size of saidsilica gel particles is on the order of 20 microns whereby the sharpnessproduced by said aluminum flakes is smoothed and a textured surfaceresults upon the application of said coating composition to a surface.

13. The coating composition claimed in claim 1 wherein at least 4% ofsaid aluminum particles are greater than 100 microns in their majordimension.

14. The coating composition claimed in claim 1 wherein said pearlsimulating agent produces a whitening effeet in the color of theresultant composition; wherein sufiicient large aluminum flakes having amajor dimension greater than 100 microns are included to produce aglittering appearance due to the reflectivity of said large particles;and wherein said silica gel particles are of sufiicient size to smooththe sharpness caused by said large aluminum particles whereby, uponapplication of said coating composition to a surface, an appearance andtexture similar to a mechanically finished metal casting is produced.

15. The coating composition claimed in claim 14 wherein said pigmentfurther comprises a trace amount of yellow toner.

16. A decorative coating for a metal surface comprising a substantiallyclear polymeric film having a pigment substantially uniformlydistributed therein, said pigment consisting essentially of (a) from 15%to 30% by weight finely divided flake aluminum particles, said particlesbeing present in sizes ranging from approximately 30 microns toapproximately 200 microns;

(b) from 30% to by weight particles of a pearlsimulating agent forwhitening the appearance of said coating; and

(c) from 8% to 15% by weight particles of silica gel, said particleshaving an average diameter of at least 10 microns wherein said pigmentis present in an amount suliicient to simulate the appearance ofmechanically finished metal.

17. A decorative covering as claimed in claim 16 whereat least asuflicient quantity of a small aluminum particles having a majordimension less than microns are included so as to provide a generallygray color;

at least a sufficient quantity of large aluminum particles are includedto provide a visible number of points of high reflectivity to all anglesof incident light;

at least a sufficient quantity of said pearl simulating References Citedagent is included to whiten the gray color provided UNITED STATESPATENTS by said small aluminum particles; and

at least a sufficient quantity of said silica gel particles 3,300,4281/1967 Schmldt 260-294 are provided having a suificient size to producea 3,234,038 2/1966 Stephens 11771 smoothly textumd surface 5 3,453,1277/1969 Marotta 61; al. 106192 18. A decorative covering as claimed inclaim 17 3455826 7/1969 Telcher et a1 wherein said covering furthercomprises a trace amount 3087827 4/1963 Klenke et 106291 f yellow tonal;3,372,047 3/ 1968 Linton 106-291 19. A decorative coating compositionfor a metal cast- 10 12/1967 McGlothhn 105-84 ing having visible markson the surface thereof, said coat- 3,264,129 8/1966 f 106290 ingpresenting a discontinuous surface and appearance 3087828 4/1963 Lmton106291 for masking said marks, said coating comprising a transparentpolymeric film-forming vehicle and a pigment, OTHER REFERENCES saidpigment consisting essentially of: Formulatlon of Organlc Coatlng,Gaynes, PP-

(a) from 15% to by weight finely divided nOIl- USPO pleafing aluminumparticles, said particles being pres- Organlc Coating Technology, y PP-1218-1222, ent in sizes ranging from approximately 30 microns P- toapproximately 200 i Technical Bulletin, Cylold Flatting Agents suppliedby (b) from 30% to by weight particles of a pearl- 2O applicant as Priorsimulating agent; and (c) from 8% to 14% by Weight particles of silicagel, ALLAN LIEBERMAN Pnmary Exammflr said particles having an averagediameter of at least R. ZAITHER, Assistant Examiner 10 microns whereinsaid pigment is present in an amount suflicient to simulate theappearance of a 25 mechanically finished metal. 106195, 288, 290; 26039M, 40, 41 B, 41 C

